Polymer is constructed by repetitive chemical bonding between low molar mass molecules. The common structures can be linear, network, or branched. Although conventional polymeric materials are generally insulators, polymers with conjugated chain structures are capable to conduct electricity by transport of pi electrons. Particularly, with the procedures of redox reactions, the conductivity of conjugated polymers can reach the levels of doped inorganic semiconductors or some conductors. This unique property, when combined with other important advantages such as low material cost, simple fabrication processes, compatibility with large area manufacturing, light weights, and bendable mechanical properties, has made conjugated polymers emerging as the vital candidate for next generation optoelectronics.
For example, PLEDs (polymer light emitting diode) are the application that is widely studied. In short, conjugated polymers are used as a kind of light emitting material, which in turn is applied between positive electrodes and negative electrodes to form light emitting films. When forward bias is applied, holes are injected into the polymer molecular film from the positive electrodes and enter valence band to become positive polarons. Moreover, electrons are injected from negative electrodes and enter a conducting band to become negative polarons. And the two polarons move in the opposing directions to be combined to emit fluorescence (visible light).
Polymer LEDs can become polymer semiconductor laser with proper design and manufacturing process. The operation principle of the polymer semiconductor laser is generally similar to that of polymer LEDs, but that the resonant cavity structure is particularly introduced and population inversion is achieved by suitable electron levels, so that when the light is transmitted in the semiconductor polymer layer, energy gap wavelength photons are stimulated to emit high intensity coherent light.
For example, the elements having the similar structure to the aforementioned structures can also be used to generate electrical power, such as using that to manufacture an electrical power generating element using solar energy. Using the energy of the photons to separate the electrons and the holes. After being separated, the holes move towards positive electrodes, and the electrons move towards negative electrodes so as to form charges needed by external circuits, and the photonic energy can be transformed into electrical energy.
No matter it's the aforementioned light emitting or electrical power generating elements, better efficiency is needed for increasing the applicability thereof.